A new deal to tackle global warming which covers all major countries is not a luxury but an "absolute necessity", Climate Change Secretary Chris Huhne has said.
Speaking ahead of the latest round of UN climate talks, which begin in Durban, South Africa, next week, Mr Huhne said the UK wanted to see a deal which included all major economies to be negotiated by 2015 "at the latest".
Such a treaty would have to be ratified by countries in time to start having teeth by 2020, as the science shows emissions need to peak and start falling by the end of the decade if temperature rises are to be kept below 2C, he said.
Efforts by the EU to secure a new deal to replace the existing climate treaty, the Kyoto Protocol, with a new legally binding global agreement failed at the crunch UN talks in Copenhagen two years ago.
The EU, which negotiates as a bloc in the UN talks, now says it is prepared to sign up for a second period of emissions cuts commitments under the Protocol when the first period ends next year. But it will only sign up to international commitments, which it says it is meeting domestically anyway, if there is agreement towards a deal which includes other major emitters who are not part of Kyoto, including the US and China.
In the face of criticism that the UK and EU's demand for parallel agreement alongside Kyoto means securing a new deal is being deferred until 2020, Mr Huhne said the EU's preferred option was a "treaty framework covering everyone now".
But with some countries calling that option premature and wanting to delay starting talks until after 2015, he said that if the conference in Durban delivered a mandate to negotiate a new treaty it would be "a significant step forward".
And he warned: "A global deal covering all major economies is not a luxury. It is not an optional extra. It is an absolute necessity.
"The UK has always been an advocate of a legally-binding agreement under the United Nations. Why? No pressing international problem has been solved without one."
Responding to Mr Huhne's speech to the Grantham Institute for Climate Change at Imperial College London, Greenpeace UK's chief policy adviser, Ruth Davis, said he had injected some "much-needed urgency into the discussions about how to achieve a new global climate deal".